1. Field of the Invention
The present invention relates to a lead-provided porous metal sheet and a method for manufacturing the same, and more particularly, to a lead-provided porous metal sheet preferably used as a spiral type electrode plate of a battery. In order to use, as a spiral type electrode plate, a porous metal sheet formed by using a combination of porous sheets such as a foamed sheet, a piece of nonwoven cloth, and a mesh sheet or only one of these three types of sheets, an active substance into pores of the porous metal sheet. In this manner, leads consisting of continuous solid metal serving as a collection element for collecting electric current is formed along the peripheral edge of the spiral type electrode.
2. Description of the Related Art
In the case of a cylindrical battery having the spiral type electrode plate, the porous metal sheet is used as the core of both positive and negative electrode plate. The band-shaped positive and negative electrode plates formed by charging the active substance into pores of the porous metal sheet are spirally wound, with a separator interposed therebetween.
In order for the battery having the spiral type electrode plate to collect electric current, and one end of a collection terminal is connected with a portion of the positive and negative electrode plates by spot welding, respectively and the other end of the collection terminal welded to the positive electrode plate is welded to a sealing portion, provided with a cap, serving as a positive terminal, and other end of the collection terminal welded to the negative electrode plate is welded to the inner bottom surface of the metal casing of the battery.
In the case where each collection terminal is connected with each electrode plate at one point thereof by spot welding, the distance between the point at which electric current has been generated in the electrode and each collection terminal is long and further, collected electric current is flowed only through one collection terminal. Consequently, the internal resistance of the battery is great.
Because the rigidity of the porous metal sheet becomes very high when the active substance is charged into pores thereof, there is a high possibility that the porous metal sheet is broken when it is wound spirally. If the lead is not broken, electric current can be collected effectively, while if the lead is broken, the porous metal sheet cannot function.
Thus, as shown in FIG. 13, a battery of multipoint collection type is proposed: A positive electrode plate 1 and a negative electrode plate 2 are spirally wound by varying the vertical position of the positive electrode plate 1 and that of the negative electrode 2 a little from each other, with a separator interposed therebetween; an upper edge portion of electrodes 1 and a lower edge portion of electrodes 2 are project respectively upward and downward from a core portion piled with electrodes 1 and 2; leads 4 and 5 made of solid metal are provided on the projected portion of the electrodes; collection terminals 6 and 7 made of metallic lath plate, a metallic net, or a metallic plate are placed on the leads 4 and 5, respectively, and the collection terminals 6 and 7 are welded to each of the leads 4 and 5. There is a case where the collection terminals 6 and 7 are connected with each of the leads 4 and 5 at one point thereof.
Methods shown in FIGS. 14A and 14B are known as the methods for forming the electrode plates 1 and 2 having the leads 4 and 5 provided at one end thereof.
According to the method shown in FIG. 14A, initially, a porous metal sheet 10 is pressed in the widthwise direction thereof at regular intervals to form lead portions 10a having pores at a very small percentage. Then, an active substance is charged into pores of the porous metal sheet 10. At this time, the active substance is not charged into the lead portions 10a because the lead portions 10a have pores at a very small percentage. Then, the porous metal sheet 10 is slitted along the lead portions 10a in the lengthwise direction thereof. Then, the porous metal sheet 10 is cut in directions perpendicular to the lengthwise direction thereof to a length necessary to be used in a battery. Thereafter, a lead plate 10b made of a narrow band-shaped metal plate is welded to each of the lead portions 10a because the lead portions 10a are thin and hence does not have a high strength. In this manner, leads 4 and 5 are formed.
According to the method shown in FIG. 14B, first, lead plates 10b made of a narrow band-shaped metal plate are welded to the porous metal sheet 10 by spacing the lead plates 10b at regular intervals in the widthwise direction of the porous metal sheet 10 to form the leads 4 and 5. Then, an active substance is charged into pores of the porous metal sheet 10. At this time, the active substance is not charged into the leads 4 and 5 because the lead plates 10b have been welded to the porous metal sheet 10. Then, the porous metal sheet 10 is slitted and cut to form an electrode plate to be used in a battery.
In the above-described electrode plate, the narrow band-shaped metal plate 10b is welded to the porous metal sheet to form the leads thereon. The metal plate 10b is very thin and the width thereof is as small as 1.0 mm-5.0 mm. Thus, it is very difficult to weld the metal plate 10b to the porous metal sheet 10 and further, welding positions are frequently dislocated from predetermined welding positions. Therefore, the electrode plate thus formed has a low accuracy.
In order to overcome the above-described disadvantage, the present applicant proposed the electrode plate having leads (disclosed in Japanese Laid-Open Patent Publication No. 3-241662). The electrode plate is made of a porous metal sheet formed by plating a combination of three-dimensional net-shaped porous sheets such as a foamed sheet, a piece of nonwoven cloth, and a porous mesh sheet layered one on the other or only one of the above three types of porous sheets which can be allowed to have porosity at more than 90%.
According to the method for forming leads on the three-dimensional net-shaped porous metal sheet, a lead-forming sheet is overlaid on the surface of a combination of porous sheets such as the foamed sheet, the nonwoven cloth, and the mesh sheet layered one on the other or only one of them, and then, plating is performed. As a result, the leads consisting of solid metal are continuously formed.
The above-described three-dimensional net-shaped porous metal sheet has porosity at more than 90% and eliminates the process of welding the metal plate forming a lead to the porous metal sheet. But it is necessary to layer the lead-forming sheet on the base sheet in plating the base sheet. Thus, it takes much time and labor to mount lead-forming sheet on the base sheet.
In addition, it is necessary to prepare a lead-forming sheet consisting of a metal foil sheet or a resin sheet having tape-shaped lead-forming portions continuously formed at regular intervals and the porous portions inter-posed between the lead-forming portions; a metal foil tape; a water-soluble film having the lead-forming portions printed with coating material, resin or metal powders; a lead-forming sheet having fine meshes in lead-forming portions and having a porosity at 40-90%, provided in portions between the lead-forming portions. Thus, the cost for manufacturing the lead forming sheet is high and takes much time and labor.
Further, in order to form the lead by plating, a masking sheet on which metal is not deposited is adhered to portions of the surface of the porous metal sheet formed by a primary plating except for the lead-forming portions thereof, when the lead is formed by plating. In addition, another masking sheet is required in forming a wide lead by a secondary plating. Thus, it takes much time and labor to install the masking sheet on the porous metal material and remove it therefrom.
Furthermore, it is necessary to provide another lead-forming sheet in altering the width of the lead or the interval between the leads.